JPS5998754A - Method and apparatus for supplying high voltage to electrostatic sprayer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention provides a direct current low voltage for supplying a high voltage to an electrostatic spray (or atomization or atomization) device, and the direct current low voltage is stabilizing to a predetermined value and setting the magnitude of the current below a predetermined threshold corresponding to a predetermined distance between the electrostatic spray device and the grounded object. , reducing the DC low voltage when the magnitude of the current exceeds the threshold, and converting the DC low voltage into a DC high voltage approximately proportional to the DC low voltage; The present invention also relates to a device for carrying out the method.

<Description of the Prior Art> Electrostatic atomization spraying is currently a well-known method of painting. In this method, the action of a large electric field on electrically charged paint droplets or solid particles is used to ensure the transport and adhesion of paint droplets or particles to the object to be painted or sprayed. .

In electrostatic spraying (electrostatic painting or electrostatic atomization) equipment, the high DC voltage required to generate the electric field is typically coupled to a regulated power supply supplying a low voltage DC current under constant voltage;
The DC low voltage supplied by the stabilized power supply is 40 to 1
It has a high voltage generator that converts it into a DC high voltage of the order of 20KVC (kilovolts). Typically, high-voltage generators in the true sense are high-frequency (several tens of KHz)
oscillator, a cylindrical frequency transformer that boosts the output voltage of the high frequency oscillator to a high frequency intermediate voltage, and a voltage obtained from the secondary side terminal of the high frequency transformer that is rectified and boosted to provide the desired output. It has a voltage summing rectifier or a voltage multiplier in a cascade connection shop for generating DC high voltage. To this effect, the output of the voltage generator is generally connected to the charging electrode via a resistor with a very large value.
The electrode is arranged on the side of a paint or powder atomizing nozzle of an atomizing device, e.g. an atomizer gun, to charge paint droplets or powder particles ejected by the nozzle and to It has the function of generating an electric field f, which has the function of transporting the paint or powder from the nozzle to the object to be coated with paint or powder.

Furthermore, the low voltage generation circuit is usually provided with a safety device in order to cause a drop in the high voltage when the current output by the generator becomes too low. Such safety devices prevent the formation of a dangerous electrical arc between the high voltage electrode and earth (the object being painted or covered with powder or any other object placed on the ground). necessary to avoid. In fact, when using an atomizing device in a flammable or explosive atmosphere (a mixture of air and paint vapors with or without solvent vapors), arcing can cause combustion or explosion of the atmosphere. Similarly, possible short-circuits between the high-voltage electrode and the worker must be avoided. Otherwise, the worker would receive a large electric shock.

A means of detecting the risk of the occurrence of a spark discharge is to detect an abnormal increase in the strength or magnitude of the current output under the damping voltage. In fact, an increase in the magnitude of the output current indicates that the high voltage electrode has come dangerously close to a grounded object and therefore indicates that the high voltage needs to be reduced or disabled. This information is commonly obtained by sampling the current from ground to the voltage generator. However, it is also possible to obtain information about the current of the low voltage current which is approximately proportional to the increase in the current generated by the voltage or is a function of the current intensifier.

Until now, the manufacturers of city voltage generators for Jingtun carving have
It is possible to manufacture a power generation device that has rectangular current-voltage characteristics, that is, the voltage remains almost constant unless the current exceeds a preset threshold, and immediately drops rapidly once the threshold is exceeded. It was common. Regarding this point, French Patent No. 1568060 (page 1 right column, last section), French Patent No. 1568060 (page 2 right column, line 27), French Patent No. 156
See No. 2917 (page 1, right column, before the last paragraph) and French Patent No. 2,036,794.

It should be noted that the last-mentioned specification shows a completely rectangular current-voltage characteristic curve.

By the way, it goes without saying that the effect of electrostatic force becomes stronger as the potential gradient of the electric field increases.Therefore, up until now, if the high voltage is maintained at a large value, it will ensure the maximum potential gradient, and It was believed that the capabilities of the high voltage generating device would be utilized in a good manner.Therefore, safety devices should be used at the point when maintaining the high voltage becomes dangerous - in other words, when the high voltage electrode is connected to a grounded object. The distance between them was controlled to take effect when the distance between the This critical distance that can vary is generally 5α
the normal distance or spacing of the other is generally 10
It is between cnL and Ome.

In any case, there are two drawbacks to the use of safety devices currently in use. A first drawback stems from the fact that safety devices are usually implemented by active electronic components.

If you fail to respond or respond incorrectly to information regarding the output current, safety is no longer guaranteed. Second
The disadvantage of is based on the fact that the high voltage is maintained at its maximum value until the safety device intervenes. By the way, a high voltage generator has elements having a non-negligible electric capacity due to its structure. If the energy stored in such capacitances is not released very quickly at the point of danger, dangerous destructive discharges can occur. The high voltage generators currently in use store this energy up to its maximum value until the point of intervention of the safety device. Therefore, if the discharge from these capacitors via the high-voltage electrodes is very slow, the risk of a spark discharge or spark generation due to a possible capacitive discharge, despite the intervention of safety devices, is very low. These are practical problems, such as inserting a very large resistor immediately upstream of the high voltage electrode, or changing the capacity of the high voltage generator and the metal element to which high pressure is applied through manufacturing. Protection measures may be taken by various means, such as reducing the voltage as much as possible or providing supplementary safety devices that act upon rapid changes in the magnitude of the output current representing rapid approach of the high-voltage electrode to earthed objects. The reality is that there are.

On the other hand, the control of the threshold at which the safety device should intervene is very complicated. In fact, the output current under high voltage includes two components: Namely: 1) Ionic current caused by corona action between the electrode and the grounded object to be coated. A portion of this current charges the pulverized paint. This current intensifies when the potential gradient between the electrode and ground increases.

2) Slow spraying from the spray nozzle to the container causes a leakage current that flows through the paint itself supplied to the gun and into the paint reservoir in the paint container. This leakage current depends on the composition of the paint.

Control of the safety device is generally carried out using a gun for atomizing applications where no paint is present, and therefore only with ionic current. For example, safety devices are generally controlled to intervene when the magnitude of the output current corresponds to a critical distance of 5α between the high voltage electrode and ground. Therefore, during work, if non-conductive paint is used, the safety device will operate at a distance of 5 degrees, but if the paint used is conductive, it will operate at a correspondingly greater distance. The device will work. This distance also increases as the resistivity of the paint decreases. For this reason, when using Enoki's conductive paints, special controls are carried out to avoid intervention of safety devices at very large electrode-to-earth distances. Such special control is a particularly delicate control determined by trial and error, and the DC braking voltage must be maintained at its maximum value up to the critical distance mentioned above.

<Summary of the Invention> The essential object of the present invention is to eliminate the drawbacks of conventional high voltage generators and to provide a high DC voltage to an electrostatic blower while ensuring great safety in terms of spark generation relative to the ground. The object of the present invention is to provide a method and apparatus for supplying the same. It is also an object of the present invention to provide an electrostatic shielding device which is less expensive and more reliable than the active electronic devices used for the safety of previously known voltage generators. The object of the present invention is to provide a device for supplying voltage.

In order to achieve the above object, the method according to the invention provides a method for generating a DC low voltage having a value which is significantly larger than a predetermined value of the stabilized DC low voltage during no current (no load). is supplied from the power supply, and corresponds to the increase in the magnitude of the current,
Gradually reducing the power supply DC low voltage from a high value to the phase vortex to a value considerably lower than a predetermined value of the stabilized DC foot voltage, so that upon reduction of the power supply DC low voltage, When the magnitude of the current reaches a predetermined threshold, the power supply DC low voltage passes through a value approximately equal to a predetermined value of the stabilized DC low voltage, so that the power supply DC low voltage Stabilizing the DC low voltage to a predetermined value when the low voltage is greater than the predetermined value, and releasing the stabilization and causing the current to decrease when the magnitude of the current exceeds the predetermined threshold. It is characterized by:

The present invention provides that, unlike what has been attempted with conventional voltage generators, the high voltage electrodes can be used on objects to be coated or This is based on the recognition that it is not necessary to maintain the high voltage at a constant maximum value when approaching all grounded objects. In fact, in conventional voltage generators that generate a constant maximum high voltage up to the critical distance mentioned above, the potential gradient is created when the high voltage electrode approaches the object to be coated while maintaining the distance greater than the critical distance. Attempts have been made to increase the potential gradient rapidly, but the inventor has found that it is not necessary to increase the potential gradient very much (a small increase in the potential gradient ensures good electrostatic effect for intermediate and small spray distances). In other words, the inventors have found that, in order to obtain a good electrostatic effect for intermediate and small spray distances, it is possible to obtain a good electrostatic effect for medium and small spray distances without a breakdown such that a spark occurs between the electrode and the ground. We have confirmed that it is sufficient to increase the potential gradient in a reasonable manner (using the output current) without increasing the potential gradient.

Therefore, the high voltage generator according to the present invention can be used in a conventional 1I
When a DC high voltage with a constant maximum value is supplied up to a distance of Jt, and the magnitude of the output current increases, in other words, when the distance between the high voltage electrode and the earth decreases,
It is arranged to supply a high voltage of gradually decreasing value for intermediate and small spray distances. From a safety point of view, the high voltage generator according to the invention has the advantage that the high voltage can be gradually reduced before the high voltage electrode reaches a distance to the ground object equal to the aforementioned critical distance. .

Therefore, when a risk of spark generation due to a very large (rapid approach) of a high voltage electrode to a grounded object arises, the voltage is already at a sufficiently low level to eliminate such a risk.

Furthermore, with the high-voltage generator according to the invention it is possible to work at normal and intermediate spraying distances with admittedly small but tolerable potential gradients, even when using electrically conductive paints. can. In contrast, known high-voltage generators of the type in which the safety device completely shuts off the high voltage cannot be operated under the same conditions. In the example of using a very highly conductive paint, the threshold at which the high voltage is gradually reduced starts from a distance equal to the distance at which the high voltage begins to decrease when using a non-conductive paint. It can be controlled so that the high voltage starts to decrease. In this case, in any case, the control of the threshold value is not so delicate or precise as compared to the case of conventionally known tube voltage generators. This is because this threshold value or adjustment is made in response to a normal spray distance, whereas previously it was made in response to a critical spray distance where the probability of spark occurrence is high.

A high voltage generator using a non-explosion EA includes a DC low voltage power supply circuit, a voltage stabilization circuit connected to the output end of the DC low voltage power supply circuit, and a voltage stabilization circuit connected to the output end of the voltage stabilization circuit. a high voltage generator that supplies a high DC voltage approximately proportional to the output voltage of a voltage stabilization circuit; means for reducing the output DC voltage of the device. According to the present invention, the low-voltage power supply circuit supplies a stabilized direct current low voltage normally generated by the voltage stabilization circuit when the current magnitude becomes smaller than a predetermined dark value under no-load conditions. It is configured to supply a DC low voltage having a value considerably greater than the value. Further, the means are configured to gradually reduce the low voltage supplied to the stabilization circuit from the substantially high value to a value substantially lower than the value of the stabilized DC low voltage. It consists of passive circuit elements or elements installed in the voltage supply circuit, so that when the low voltage decreases, when the magnitude of the current reaches the predetermined threshold value, the stabilized DC low voltage is activated. The low voltage passes through a value approximately equal to the value. Note that the predetermined threshold value corresponds to a predetermined operating distance of the electric ejection device with respect to a grounded object.

As will be explained later, the passive element can be constructed from a simple resistor that is much cheaper than the active electronic safety devices used in conventionally known voltage generators and has much higher reliability. I can do it.

DESCRIPTION OF THE EMBODIMENTS Other features and features of the invention will become apparent from the following description of preferred embodiments of the invention, which are illustrated in the accompanying drawings.

The voltage generator shown in FIG. 1 is equipped with a transformer 1 similar to the known one, and its downstream side 2 is, for example, 220M l'
It is connected to a low-voltage AC power source with a commercial frequency such as 50 Hz. The alternating voltage (2) obtained at the terminals of the secondary winding 3 of the transformer 1 is rectified by a rectifier circuit formed by a device such as a diode 4, and then filtered by a smoothing capacitor 5. capacitor 5
The DC voltage V2 obtained at the terminal is applied to the input terminal of the voltage stabilizing circuit 6. The voltage stabilizing circuit 6 generates a stabilized DC low voltage (4) of, for example, 10 volts at its output terminal. This voltage 4 is applied to the input of a high voltage generator 70, and the Km pressure generator has a voltage 4 applied to its output.
For example, 40000 to 1200 [10V
(Volt) DC high voltage VHT is generated. The output end of the high voltage generator 7 has a very large value (several tens of megaohms)
is connected via a resistor 8 to a high-voltage electrode 9 of a comminution device, such as an atomizer gun (not shown). As is known, the resistor 8 and the high-voltage generator 7 can be housed together with the atomizing gun, while the other elements 1 to 6 of the pressure generator can be spaced apart from the atomizing gun. A low voltage cable connects the spray gun to the spray gun. FIG. 1 schematically shows an object 10 to be painted or coated with powder, which object 10 is grounded.

All elements mentioned above are well known and therefore need not be explained in detail. To briefly describe the high voltage generator 7, this generator I consists of a high frequency (several tens of kHz) oscillator and a transformer that increases the output voltage of the high frequency oscillator to a voltage intermediate to the high frequency. and a type of power rectifier or voltage multiplier that refers to a rectifier and a capacitor for rectifying the high frequency intermediate voltage supplied by the transformer and increasing it to the desired flat DC voltage VHT. It is useful to configure
It is. Also, as is well known, by using the ^frequency, it is possible to reduce the capacitance of the voltage multiplier capacitor, thereby making it possible to miniaturize the capacitor and house it in the gun for atomization spraying. becomes possible.

This miniaturization makes it possible to further reduce the electrical output of the high-voltage generator, which in turn makes it possible to reduce the capacitive energy stored in the capacitor, which is especially true. , is important in ensuring safety in the event of a possible short circuit to ground.

According to the present invention, the secondary winding 3 of the transformer 1 is controlled by the voltage stabilizing circuit 6 so that the DC low voltage v2 obtained after rectification by the diode 4 and smoothing by the capacitor 5 is normally It is designed to supply an alternating current low voltage Vl of such a value that it can have a value considerably higher than the value of the generated stabilized direct current low voltage V4.

For example, if a stable voltage of 10 volts is to be supplied by the voltage stabilizing circuit 6, the secondary winding 3 of the transformer 1 is designed so that the resulting no-load voltage V2 is equal to 24 volts. can do.

Further according to the invention, resistor 11 is connected in series between diode 4 and voltage stabilization circuit 6. This resistor 11 adjusts the low voltage 3 supplied to the voltage stabilizing circuit 6 from the value of the DC low voltage (10V) stabilized from the voltage 2 as the magnitude of the current increases. The value of resistor 11 is determined by the value of resistor 11 when the magnitude of the current is reduced to a pre-controlled threshold value.
The voltage v3 is selected such that when decreasing it passes through a value approximately equal to the value of the stabilized DC low voltage v4 (plus the voltage drop ΔV in the voltage stabilization circuit 6). This corresponds to the normal use or operating interval of the electrostatic copying device for objects that are being used. With a voltage drop ∆■ of about 6 volts, the threshold voltage is applied to the high voltage electrode 9 and 'FJfl
Corresponding to a distance of approximately 10 CIIL to the painted object 10, and assuming that 0.5 amperes are selected in the absence of paint (as shown in FIG. 2), the resistance of resistor 11 is 22 ohms. It will be given a value.

Under practical operating conditions with paints that are more or less conductive, high wave currents flow through the paint to earth. This current is caused by the ion' between the electrode 9 and the object to be coated 10.
It will be added to Kuryu. As a result, the average price is actually 1007
This will correspond to a distance greater than 11, and the value of this distance or spacing can vary depending on the conductivity of the paint. However, in most cases, this is not military spending. This is because when the magnitude of the current exceeds the threshold value, the voltage generator of the present invention supplies a high DC voltage with a value sufficient to obtain a light potential gradient in the coating. be. Similarly, in limited cases, for example when using paints with very high conductivity, the threshold ■. It is always possible to control the threshold value in such a way that it corresponds to an electrode-to-ground distance lying between about 10 cm and about 3DcrnO. This means, for example,
The value of voltage Vl and therefore also the value of ■2 can be changed to a slope of voltage 1 mv3 (Fig. 2), for example by using a transformer with a multi-tapped secondary winding and/or by varying the value of resistor 11. It can be realized by controlling.

Similarly, electrode 9 is a threshold value. When the object 10 is located at a distance (10 cIn or more) slightly greater than the distance corresponding to It remains at a value exceeding the required voltage value (13 volts in this embodiment), and therefore the output voltage V4 of the stabilizing circuit 6 remains at a value equal to one foot, which in this embodiment is 10 volts.

Further, the DC high voltage ■HT, which is proportional to the voltage ■4, is also constant. On the other hand, when the distance between the electrode 9 and the object 1o becomes shorter than the distance corresponding to the threshold value -, the voltage 3 becomes an insufficient value for the stabilization circuit 6 to operate normally, and as a result, The output voltage V4 increases as the magnitude of the current increases as the electrode 9 approaches the object 10.
It decreases linearly from the point where there is a difference of Δ■. The DC voltage V4, which is proportional to the voltage V4, also decreases in the same way. This reduction in the high voltage VHT occurs before the electrode 9 reaches a critical distance (approximately 5 crrt) at which a short circuit can occur between the electrode 9 and the object 1o. When the electrodes 9 are at different critical distances, the high DC voltage is sufficiently low that a possible short circuit or grounding is no longer dangerous.

Threshold work. Even if VHT is exceeded and the DC high voltage VHT is reduced, the potential gradient is maintained at a value sufficient for painting.

This is because a few high-voltage VHTs have electrodes 9 and objects 10.
This is because it is compensated for by the decrease in the distance between them.

From a safety point of view, the voltage V
It is advantageous to set a sufficiently large voltage difference between V2 and the stable voltage V4. In fact, in this case it is possible to use a resistor 11 of suitable value to ensure a sufficiently rapid drop in voltage V3 (linear slope V3 in FIG. 2), so that the magnitude of the current is below the threshold value. Engineering. It is possible to ensure a sufficiently rapid drop of the voltage V and thus also of the DC high voltage vHT when it exceeds . Conversely, the potential gradient is the threshold value. With a sufficiently higher value, the voltage 13 and therefore the voltage 4 and the high DC voltage VHT do not have to decrease in a very rapid manner. Therefore, the selection of the value of the pressure v2 as well as the value of the resistor 11 is made as a compromise between the two considerations mentioned above, and the desired threshold value is determined.

Therefore, the linear high voltage ■□0 is gradually reduced depending on the value of the distance from which it is started.

The embodiments of the present invention described above are provided purely as examples and are in no way intended to be limiting (although numerous modifications can easily be made by those skilled in the art without departing from the scope of the present invention). For example, instead of installing the resistor 11 in series between the diode 4 and the voltage stabilizing circuit 6, the secondary winding of the transformer 1 can be connected as shown by the dotted line in figure g1. It is also possible to provide the transformer 1 in series between the resistor 3 and the diode 4.The resistor 11 may be omitted and the transformer 1 of the saturated iron core type has the characteristic of providing a voltage inversely proportional to the generated current. could be used. In this case, voltage 1 would vary in the same way as voltage V3. Furthermore, in the voltage generator shown in FIG. 1, transformer 1 and diode 4
It would also be possible to replace it with a 24 volt storage battery, for example.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram schematically illustrating a high-voltage generator for a silent singing device to which the present invention can be applied, and FIG. 2 is for explaining the operation of the voltage generator shown in FIG. 1. FIG. 1...Transformer, 2...-secondary winding, 3...secondary winding, 4...diode, 5...capacitor, 6...
Voltage stabilization circuit, γ... High voltage generator, a, ii...
-Resistor, 9...High voltage electrode, 10...Object to be painted.

Claims (1)

[Claims] (11) In order to supply a high voltage to the electrostatic spray device, a DC low voltage is supplied, the DC low voltage is stabilized at a predetermined value, and the magnitude of the current is set to a value lower than a predetermined darkness value corresponding to a predetermined distance between the electrostatic spray device and a grounded object, and when the magnitude of the current exceeds the threshold value, the Reduce DC low voltage,
In the method for supplying a high voltage to an electrostatic spray device, which includes converting a low DC voltage into a high DC voltage approximately proportional to the low DC voltage, when no current flows (no load), , supplying a DC power supply low voltage having a value significantly higher than a predetermined value of the stabilized DC low voltage;
gradually reducing the DC power supply low voltage from the substantially high value to a value substantially lower than a predetermined value of the stabilized DC low voltage in response to a current strength intensifier;
When the DC power supply low voltage decreases, the DC power supply low voltage passes through a value approximately equal to the predetermined value of the stabilized DC low voltage when the magnitude of the current reaches the predetermined threshold value. Therefore, when the value of the DC power supply low voltage is larger than the predetermined value, the DC low voltage is stabilized at the predetermined value, and the current magnitude is adjusted to the above predetermined value. A method for supplying a high voltage to an electrostatic spray device, characterized in that the low DC voltage is deregulated and reduced when a predetermined threshold value is exceeded. (2) A power supply circuit C1, 4) that supplies low voltage DC in order to supply high voltage to the electrostatic spray device, and a voltage stabilization circuit (6) connected to the output end of the low voltage DC power supply circuit. and,
a high voltage generator (7) connected to the output end of the voltage stabilization circuit (6) for supplying a DC high voltage substantially proportional to the voltage of the voltage stabilization circuit; means (11) for reducing the output voltage of the voltage stabilizing circuit (6) and therefore also the output DC high voltage of the high voltage generator (7) when a set threshold is exceeded; The DC low voltage power supply circuit CI, 4) is
a value considerably higher than the regulated DC low voltage (v4) normally supplied by said voltage stabilization circuit (6) when the magnitude of the current is less than a predetermined threshold thereof (
V2) at no-load, and the means (11) is configured to supply a low DC voltage (3) supplied to the stabilizing circuit (6) to the corresponding voltage. A passive circuit element provided in the DC low voltage power supply circuit C1, 4) so as to gradually decrease from a high value (V2) to a value considerably lower than the stabilized low voltage value (■4). 2, whereby the low voltage (3) becomes a stabilized DC low voltage when the magnitude of the current reaches the predetermined threshold (S) upon its reduction. (differing by Δ■)), said predetermined threshold value (d) corresponding to a predetermined working distance of the electrostatic spray device with respect to a grounded object. A device for supplying high voltage to an electrostatic spraying device, characterized in that: (3) the DC low voltage power supply circuit includes an AC low voltage power supply, a transformer (1), and a rectifier circuit (4); The secondary winding (3) of the transformer (1) is connected to the rectifier circuit (4).
The electrostatic capacitor according to claim 2, wherein the electrostatic capacitor is configured to supply an AC low voltage having a value (■1) such that the output 4 of the resulting DC low voltage has the large value (■2). Device for supplying high voltage to spray equipment. (4) The electrostatic charge according to claim 6, wherein the passive circuit element (11) is a resistor installed in series between the rectifier circuit (4) and the voltage stabilization circuit (6). A flexible device that supplies high voltage to the spray device. (5) The passive circuit element (11) is the secondary winding (3)
7. A device for supplying high voltage to an electrostatic spray device according to claim 6, which is a resistor connected in series between the rectifying circuit and the rectifying circuit. (6) Claim 6, wherein the passive circuit element (11) is comprised of a transformer (1) that is a saturated iron core transformer.
A device for supplying high voltage to the electrostatic spraying device described in 1.